Title: Thermal Inactivation of Salmonella in Commercially-Processed Liquid Egg Yolk Authors
|Jordan, Johari - DEL. STATE STUDENT/FSIT|
|Marks, Harry - USDA, FSIS, OFDER|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 2009
Publication Date: May 17, 2009
Citation: Jordan,J.,Gurtler,J.,Marks,H.,Jones,D. 2009. Thermal Inactivation of Salmonella in Commercially-Processed Liquid Egg Yolk [abstract].American Society of Microbiology 109th General Meeting.Philadelphia,PA.p.1. Technical Abstract: The Egg Products Inspection Act of 1970 regulates egg products through the USDA Food Safety and Inspection Service (FSIS) by mandating minimum thermal pasteurization requirements for specified egg products. These standards were based on data for the inactivation of Salmonella in liquid egg products acquired prior to 1970 and are currently being reevaluated in light of recent risk assessments, which take into account changes in industrial practices such as in-line egg processing and variation in egg product formulations. The goal of this study was to determine the inactivation kinetics for a cocktail of thermally-resistant, poultry-associated strains of Salmonella inoculated into commercially-processed liquid egg yolk. Three heat-resistant strains of Salmonella Enteritidis (two of phage type [Pt] 8 and one of Pt 13) and one strain of serovar Oranienberg were selected for resistance to 50 ug/ml nalidixic acid. Cultures were grown to stationary phase in Tryptic Soy broth at 42 deg C, with one 24 h transfer, concentrated ten-fold by centrifugation, and resuspended in 0.1% peptone water. Each inoculum was added to commercially-processed liquid egg yolk and mixed thoroughly, resulting in a final population of ca. 8 log CFU/ml egg yolk. Inoculated yolk was injected into sterile glass capillary tubes, flame-sealed and heated in a water bath at 58, 60, 62, and 64 deg C. Capillary tubes were ethanol sanitized, rinsed twice in sterile water and contents were extracted. Yolk was diluted, surface plated onto Tryptic Soy agar + 0.1% sodium pyruvate and 50 ug/ml nalidixic acid and incubated at 37 deg C for 24 h before colonies were enumerated. Decimal reduction values were calculated from survivor curves with a minimum inactivation of 6 log CFU/ml at each temperature. The D values were 2.95 min at 58 deg C, 0.98 min at 60 deg C, 20.80 sec at 62 deg C, 6.88 sec at 64 deg C. These values are in agreement with or slightly higher than what been reported in the literature for egg yolk pasteurization. Ongoing studies are examining inactivation at 66 deg C as well as fitting yolk pasteurization data to a mathematical model.